Blog & User Creator

I'm guessing this can be resoved in the main functions.php file, but I'm attempting to add blogs for existing student users. The problem is we've used their student ID numbers as their usernames. I get an error stating that blog/user names must have letters too when using the blog/user creator plugin. Obviously, I was able to create user accounts (without blogs) using just student id numbers. Any thoughts on what I need to change to enable blogs to be associated with these users?